Annealing of sheet steel



Dec. 14 1926.

H. S. M'ARSH ET AL ANNEALING 0F SHEET STEEL F'iled Oct. '7, 1925 2Sheets-Sheet s n W w Dec. 14 1926. 1,610,567

H. s. MARSH ET AL ANNEALING OF SHEET STEEL Filed Oct. 7, 1925 2Sheets-Sheet 2 /N VEN TORS W l TNE'SSES "fum Pezenas Dec. 14,1926,

UNITE-.D STATES HENRY s.

PjA'rlzN'r oFFficE. A

BALB' B, OOUHBAN, 0F YOUNGBTOWN, OHIO.

"mamme 4on' sanar srnnr..

Application med Uetobor?, 1925. Serial No. 30,978.

ylow temperature. that the crystals or grains are badly distorted, andconsell qliliently it becomes necessary to anneal the eets after theyhave 4been rolled, in order to restore the normal grain structure, andrender the sheets suitable for the .drawing operations which at the,present day are widely practiced. Some" years ago rolled, steelsheetswere ordinarily box annealed: 'But box annealing gives widely varyingresultrs; sometimes the annealed sheets are very sti and sometimes theyare of loaden y softness. and the product'yvhich approacheseitherof-these extremes is unsuitablefor-the drawin trade. A laterpractice has been to-blu anneal sheets, which are intended to be used indrawing operations, and some- 3 timesto bei: anaiealafterwards. Butstill the resultsI are erratic and not to be depend- 5ed on: boxannealing causes gram growth, 'and sheets which are blue annealed aresub- I ject toscalingl The consequent roughness of 'surface cannot beentirely eliminated in subt F sequent cold rolling.

Such, however, are the limitations 'under t lwhich the art hasprolgressed4 hithertoi and the trade is constant v demanding o f the lsteel makerl better-and 4better sheets. Our

process overcomes these limitations. -V

We ,iirst heat the rolled sheet material in a non-oxidizingatmosphere tothe requisite high temperature, which for ordinary comvmereial.steels is'fro1n 17509....to 1800 F., preferably to the "higher figure; and then,while'still maintaining the non-oxidizing at- Inosplmre, we .coolitagain through a range of 290 to 300do'wnward from. the maxiindicated.Having accomplished this,

method whereby' we allow thev cooling Vto proceed with no furtherconcern tomamtan a non-oxidizing atmosphere, and preferably in the lopenair, until the material comes to. a dull red heat. At this .tenperaturewe pass the sheets through a'ro er leveler. which attens them, andincidentally cools them through another hundred degrees, more or less.'Vlfe then make the sheets up into packs of from three to six inchesthick; they are then of just visible redness. And we then set 4the packsaside tov cooLto atmospheric 'tem rature.

The initial steps of heating an cooling in a non-oxidizing atmosphere mabe carried out in a continuous furnaceof he ordinary open-type, modifiedto serve the ends described. Thron h the furnace shown in the drawingsthe sheets advance .from left to right. V.The furnace toward .the intakeend is provided with burners 1, through which flame-has ingress, and inthe proper'operation of the furnace the llame ywill be of non-oxidizingcharacter, or substantially so,4

and under ordinary conditions of 4operation such ingress of air asoccurs still leaves the atmosp ere within the furnace substantiallyneutral., Thefurnace stack 2 is to the right, and the flow of flame andhot gases is in the direction of the ladvance of the material,

from ,left to right.

The furnace is made much lon r than such furnaces ordinarily are, antoward the delivery end there is no inflow of llame. Toward the deliveryend accordingly the stream of gases, non-oxidizing in character, is.cooling ing up their'heat and becoming cooler.

Furnace strpcture and operation will vary in detail, to suit .thecharacter of the material which is habitually'or .occasionally runthrough it. For instance, when thick sheets are being annealed -ent-highspeed, relativel large quantities of heat are given up to an absorbed bvthe walls at the cold end of the furnace. To meet such a condition, 'thefurand the advancing sheets are giv.

.nace walls may be made thin, and pipes of familiar construction may beprovided withy in the furnace walls, for the circulation `of water, tocarry away the excess heat, perhaps regularly, perhaps whenspeciallyrequired. With like ends in view, a bridge wall, such as is indicated at3, Fig. II, ma be provided within the furnace, to absor and reflectheat,-and render the cold end of the furnace cooler, while operationprogresses.

Temperature conditions within the furnace may be. observed by means of aradiation pyrometer, and furnace operation controlled accordingly.

Typically we so proportion the parts of the apparatus which we employ,and we drive our conveyer at such speed, that the steps of iouroperation proceed as follows: heating quickly, within an interval offrom 2 to 7 minutes in a nearly neutral atmosphere, to a temperature of1700* to 1850 F.; cooling quickly, within an interval of from 1/2 minuteto 2 minutes, and still in a nearly neutral atmosphere, to a temperatureof 1200 to 1400* F.; continued cooling quickly (and conveniently in theopen air) in about l to 2 minutes, to dull red: roller leveling; thencooling slowly in 1 to 3 hours, in packs, in the open air, to atemperature of 200 F. or less.

After performing the annealing operation described, the sheet ordinarilyis pickled before use.

Certain details remain to be mr articularly mentioned. Variations inshee thickness are in ordinary practice substantially offset by varyingaccordingly the number of sheets which are caused to pass at oncethrough the furnace. When we anneal 11- gauge sheets, we pass themthrough, one at a time. We ordinarily pass. ifi-gauge sheets through,two at a time; and 20gauge, three a't a time. Finer adjustment may beeffected by varying the speed of the conveyor. Thin sheets, if runsingly would heat too rapidly and would chill before they could be madeup in packs. 4The cooler `the sheets when made up in packs, the thickerthe packs can be made, without too much softening. y

When making up the pack, the {irstsheet alone tends'to cool rapidly, butthe superposition of successive sheets arrests the fall of temperatureand undue chilling is prevented. The 6-inch ,pack is the practicaloptimum. The more sheets in a pack, the fewer lifts of the cranerequired for setting them aside to cool; but, in a 12-inch pack, forinstance, cooling proceeds so slowly that the sheets tend ultimately tobe softer than we desire them to be. The outermost sheets are, ofcourse, always cooler than those within the pack, but there is apermissible range within which the cooling step may proceed. And we havefound, all things considered, that a 6-inch pack is best.

Our invention may be practiced with some refinement in detail, toproduce a sheet of still better drawing quality, `in case the userequired of it can justify the somewhat greater cost. In this case thefurnace is made very tight, in order to Vkeep out all air, and acompletely reducing atmosphere is maintained within the furnace. Andpotection in a reducing atmosphere may prolonged to the nontarnislimgdegree of approximately 400 F. In this case cooling will preferably beso controlled as to be achieved in five to ten minutes. The sequence intreatment then is: hot roll roller level, ickle, cold roll, anneal. Inthis case, it wi be observed, ickling after annealing is not required.ickling as a. last operation (particularly when the sheets areimmediately to be put on the drawing press, as when' t e customer doesthe pickling) sometimes renders the metal brittle. Heating removes suchbrittleness, supposedly by driving out .occluded hydrogen. Anotherreason why ultimate picklin is advantageously avoided, is that when t esheet is under the drawing operation subjected to tensile stress, smallsurface depressions, such as are incident to picklin tend to weaken themetal irregularl sheet will during the rawing over the corner of the diewit less resistance than a rough one, and in that respect the danger ofa break in the sheet is diminished. From this it is clear that a smoothsheet, annealed after cold rolling, is better than a rough sheet,pickled after annealing. Such is our preferred procedure, when thecustomers job is such as to warrant the extra expense of cold rolling,and the maintenance of a furnace with air-tight walls.

We claim as our invention:

1. The method herein described of annealing sheet steel which consistsin heating the sheet material in a non-oxidizing atmosphere to atemperature of 1750 F.4 as a minimum, cooling the material whileVmaintaining it still in a non-oxidizing atmosphere to a temperature of-1550" F. as a maximum, cooling it ythence to a dull red in the openair, making the material at the temperature last indicated into packs,and allowing the packs to cool in the air toy atmospheric temperature. Y2. The method herein described of annealing sheet steel which consistsin heating the sheet material within aumaximuniV time interval of sevenminutes and while maintained in a non-oxidizing atmosphere to atemperature of 17 50 F. as a minimum, cooling the material within amaximum interval of two minutes and `while still maintained operationslip gain, a smoothin a non-oxidizing. atmosphere to a temperature of1550 F. as a maximum, and then completing the cooling in the openair.

3. The method herein described of annealing sheet steel which consistsin heating the sheet material within a maximum time interval of sevenminutes and while maintained in a non-oxidizing atmosphere to annealingtemperature, cooling the material within a maximum interval of twominutes and while still maintained in a non-oxidizing atmosphere to atemperature of 1550o F. as

a. maximum, cooling it further and within a. maxlmum time lnterval oftwo minutes set our hands.

HENRY S. MARSH. RALF S. COCHRAN.

i atmosphere to a temperature of 1550o F. as

to dull red, then making thc material into packs, and allowing the packsto cool in the air to atmospheric temperature.

In testimony whereof We have hereunto set our hands.

HENRY S. MARSH. RALF s. COCHRAN.

a maximum, cooling it further and Within a maxlmum tlme interval of twominutes DI 8O I Al M E R 1,610,567 .`-Henry S. Marsh and Ralf S.Cochran, Youngstown, Ohio. ANNEALING oF SHEET STEEL. APatent dated-December 14, 1926. Disclaimer filed March 28, 1935, by the asslgnee,Swface Combustion Corporation.

claim 2 of the said Lettersl Patent, except upon ordinary commercial theresult. and eflectJ of gaining relatively high ductility.

[Ojicwl Gazette April 2 1.935.]

steel, and with DISCLAIMER 1,610,567.'Henry S. Marsh and Ralf S.Cochran, Youngstown, Ohio. ANNEALING or SHEET STEEL. .Patent datedDecember 14, 1926. Disclaimer filed March 28, 1935, by the assignee,Sudace Combustion Corporation. Therefore, enters this disclaimer to anyperformance of the method recited in claim 2 of the said Letters Patent,except upon ordinary commercial steel, and with the result. and effect.of gaining relatively high ductility.

[Oficial Gazetie April 23, 1935.]

